An interface identifier in Ethernet (registered trademark) is generated by conversion of a MAC (Media Access Control) address of a device into EUI (Extended Unique Identifier)-64 format. Therefore, an interface identifier involves a problem that a MAC address of a device can be calculated backward from an IPv6 (internet protocol version 6) address with ease, so that the interface identifier might be used for illegal attack from the outside.
As a countermeasure to this problem, for example, Patent Literature 1 discloses an apparatus intended to ensure security by preventing use of an address in EUI-64 format in advance. Patent Literature 2 discloses an apparatus for preventing a packet that uses an address in EUI-64 format through filtering.